1. Technical Field
The present invention relates to a droplet discharge device and a method for forming a thin film.
2. Related Art
There are conventionally known techniques for forming a thin film that use a droplet discharge device. A typical example of a thin film formed using a droplet discharge device is a luminous layer of a color filter or an organic EL panel. In thin film formation techniques that use a droplet discharge device, very small droplets can be coated in a desired position in accordance with the resolution of the droplet discharge head that is used. Accordingly, a much finer pattern can be formed than achieved with relief printing and other printing techniques. For example, when a red, green, and blue color filter is formed on a color filter substrate, a color filter can be formed by discharging a solution containing red, green, and blue coloring material from very small nozzles onto a substrate, and then drying and solidifying the coloring material (e.g., see Japanese Laid-Open Patent Application No. 2002-196127 and Japanese Laid-Open Patent Application No. 2006-289765).
Recently, a method has been developed for manufacturing a color filter substrate for a plurality of models by forming a color filter (panel region) for a plurality of models on a single large substrate and then dividing the substrate into separate models. In this method, a color filter substrate for a plurality of models can be fabricated using a single droplet discharge device, and the capital expenditure will thereby be lower than if a separate droplet discharge device has to be provided for each model. Since wasted space on the substrate can be reduced by manipulating the arrangement of each panel region, the material utilization ratio can be improved.
Considered below is the case in which a plurality of color filters 303 arranged in a punctate formation are formed using the droplet discharge method on a plurality of pixel regions PX positioned on the surface of a substrate 301, as shown in FIG. 18(b). In this case, the color filters 303 are formed in desired positions by, e.g., selectively discharging ink; i.e., color filter material, from a plurality of nozzles 304 while scanning droplet discharge heads 306, which have a nozzle row 305 in which a plurality of nozzles 304 is arranged in a row, in the main direction for a plurality of cycles (two cycles in FIG. 18(b)) as indicated by the arrows A1 and A2.
The color filter 303 is formed by arranging the colors R, G, B, or the like in a stripe arrangement, a delta arrangement, a mosaic arrangement, or another suitable arrangement mode. In the ink discharge step, droplet discharge heads 306 for discharging single colors of R, G, and B are provided in advance for the colors R, G, B, or the like, as shown in the drawing, and an array of the three colors R, G, B, or the like is formed on the single substrate 301 using the droplet discharge heads 306 in sequence.
The ink discharge amount is uneven in the nozzles 304 constituting the nozzle rows 305 in the droplet discharge heads 306, with discharge characteristics (discharge amount distribution) Q typically being demonstrated; i.e., a large discharge amount occurs in positions that correspond to the two ends of the nozzle rows 305, the second largest amount occurs in the center portions, and the lowest discharge amount occurs in the intermediate portions therebetween, as shown in FIG. 18(a).
Accordingly, when the color filter 303 is formed to a predetermined thickness by the droplet discharge heads 306, nonuniformity occurs in the ink arrangement amount (film thickness) among a plurality of the color filters 303 aligned in the sub-scanning direction orthogonal to the main scanning direction of the droplet discharge heads 306, due to nonuniformity of the ink discharge amount of the nozzles 304 constituting the nozzle rows 305. In this case, problems occur in that the planar light transmission characteristics of the color filter are uneven because stark striping (arrangement nonuniformity) is formed, e.g., in the positions P1 that correspond to the ends of the nozzle rows 305, the center position P2, or both positions P1 and P2. Also, such striped arrangement nonuniformities are highly visible and lead to a loss of image quality displayed via the color filters 303.
In view of the above, a method has been proposed in Japanese Laid-Open Patent Application No. 2002-196127 in which the nozzle rows 305 are divided into a plurality of groups and the amount of ink discharged from the nozzles 304 is controlled for each group. In accordance with this method, the ink discharge amount can be made more uniform among the nozzles 304 while the circuit configuration and the work of selecting the correction value can be simplified because the amount discharged by the nozzles 304 is adjusted for each group rather than for each nozzle 304.
On the other hand, nonuniformity of the discharge amount in the droplet discharge heads 306 is also caused by variation in the discharge pattern in each main scan. A discharge pattern is a combination of nozzles that discharge (discharging nozzles) and nozzles that do not discharge (non-discharging nozzles) among the plurality of nozzles 304 provided to a single droplet discharge head 306.
For example, when ink is discharged in only the pixel regions PX of the substrate 301, the nozzles 304 over on the pixel regions are used, and the nozzles 304 over the non-pixel regions are not used. Therefore, when the droplet discharge heads 306 move in the sub-scanning direction, the spatial arrangement between the nozzles 304 and the pixel regions becomes offset, and the combination of the discharge nozzles and the non-discharge nozzles; i.e., the discharge pattern, changes.
The reason that the spatial arrangement between the nozzles 304 and the pixel regions PX becomes offset when the sub-scan is carried out is that the movement distance in the sub-scan is carried out based on the interval between the nozzles of the droplet discharge heads 306. In other words, the sub-scan is designed to be carried out for a distance that is an integral multiple of the interval between nozzles. In the case that the sub-scan is set to an integral multiple of the interval between nozzles, the spatial arrangement between the nozzles 304 and the pixel regions PX is different for each main scan because the arrangement interval of the pixel regions PX is generally not an integral multiple of the interval between nozzles. Accordingly, cases occur in which nozzles arranged in the pixel regions PX in the main scan prior to the sub-scan are arranged in regions between pixels (non-pixel regions) in the main scan following the sub-scan, which produces a difference in the discharge pattern.
The discharge characteristics Q of the nozzles 304 also change when the discharge pattern changes. The change in the discharge characteristics Q produce structural crosstalk and electrical crosstalk in the droplet discharge heads 306. In other words, the discharge amount of adjacent nozzles 304 fluctuates due to mechanical vibrations and pressure transmission via the ink when the nozzles 304 are driven, and due to distortions (overshooting and undershooting) in the drive signals fed to the nozzles 304.
In order to solve such problems, a method is proposed in Japanese Laid-Open Patent Application No. 2006-2897652 for correcting the drive waveform fed to the drive elements of the nozzles 304 in accordance with the ratio of the number of discharge nozzles (number of discharge nozzles/total number of nozzles); i.e., the nozzle duty. In accordance with this method, it is possible to prevent fluctuations (electrical crosstalk) in the discharge amount of adjacent nozzles 304 caused by distortions in the drive signal fed to the nozzles 304.